1. General Background
Broadly described, the field of prosthetics involves the replacement of missing body parts with artificial ones. Extremity prosthetics entails the substitution of an artificial limb for a lost extremity.
While many aspects of extremity prosthetics are critical to function, perhaps the most important aspect is suspension. The manner in which an artificial limb is suspended or attached to the residual limb determines the amount of control an amputee has over the prosthesis. The greater the weight and size of tissue loss due to amputation surgery, the more critical the method of suspension becomes. The method of suspension is particularly crucial to above-knee amputees, as above-knee amputations result in the largest percentage of amputees with the greatest amount of tissue loss.
Above-knee prostheses were originally suspended by some form of bulky strap or belt arrangement. The amputee would wear a sock on the residual limb to protect the skin tissue from the inner surface of the prosthesis, called the socket interface. The socket interface was usually made of wood and could irritate the skin, thus necessitating the use of the protective sock. The sock allowed the residual limb to easily slide into, as well as out of, the socket interface. This feature resulted in a fairly simple donning and doffing of the prosthesis. While this method of suspension is still applicable today, it has many well-known limitations and compromises.
Artificial limbs using suction sockets are now preferred. Suction sockets fit tightly around a patient's residual limb and are retained upon the residual limb by differential air pressure. An area of negative pressure between the residual limb and the distal end of a suction socket functions to hold the prosthesis upon the limb during use. This suspension method is the most advantageous for the amputee. It gives the amputee the ability to better control the prosthesis and provides for the greatest sensory or proprioceptive feedback. Suction suspension also makes a prosthesis feel lighter as compared to other forms of suspension. Since the introduction of suction as a viable means of suspension, it has found widespread use in virtually all levels of amputation.
Due to the numerous benefits associated with suction suspension, all amputees hope to gain the advantage of that form of suspension. Unfortunately, the amputees that are physically the least able to manage suction suspension are those who could benefit most from the advantages that suction suspension provides.
The problem lies in the donning (putting on) and doffing (taking off) of the suction socket. Donning and doffing a suction suspension prosthesis using conventional techniques is a rigorous affair too difficult for elderly, overweight, blind, arthritic, or muscularly weak patients to perform. Until now, the inability of these patients to don a suction socket prosthesis has denied them of its many advantages.
2. Conventional Donning Methods
Since the development of user-friendly suction socket fabrication techniques, this suspension method has been refined and adapted to many levels of extremity amputation. For purposes of illustration, the following discussion focuses on above-knee prosthetics, since this level of amputation best portrays the problems solved by the present invention. It must be understood, however, that the present invention is applicable to all suction suspension devices.
The combined development of removable air valves that seal against a freely machined insert in the distal end of a suction socket and donning techniques that allow an amputee to wear a prosthesis with no sock between their skin and the inner surface of the prosthesis resulted in a tremendous evolutionary step forward in prosthetic donning. The air valve allows for the creation and maintenance of an area of differential air pressure between a residual limb and the distal end of a suction socket, while a close fit between the walls of the socket and the residual limb skin maintains the integrity of the pressure differential. This pressure differential works to hold the prosthesis upon the limb. Many different valve and insert combinations have been made available, all having one thing in common--an opening of about one inch in diameter at the distal end of the socket that facilitates the use of a pull sock or bandage wrap to pull the residual limb into the socket of the prosthesis.
The donning techniques used in conjunction with pull socks and bandage wraps, however, require significant amputee balance, strength and mental acuity. In the case of a pull sock, the amputee pulls a tube stocking three feet long up the thigh to near groin level. The remaining length of this tube stocking material is hanging off of the residual limb. The hanging end of the stocking is inserted into the prosthesis at the trim line level and is pulled through the valve insert at the distal end of the socket to reduce slack in the pull sock. The amputee then stands on his sound leg and lets the residual limb, with the pull sock on, slip as far into the socket as it will easily slide. The amputee then again pulls slack out of the portion of the pull sock exposed through the valve housing. At this point the amputee is ready to begin the donning process that occurs as a result of controlled pulling on the free end of the residual limb just to the point that the pull sock begins to slip on the skin, at which point the residual limb is pulled a little deeper into the socket. This motion is repeated until the stocking is fully pulled through the valve housing and the amputee is able to see or feel with the end of the finger that the skin tissue is protruding into the valve housing. Once the amputee has reached this point, the valve body is installed which seals the suction so that they are free to ambulate.
The difference with the elastic bandage/wrap donning technique is that applying the elastic bandage wrap requires the ability to perform several circumferential wraps of the band around the residual limb with a generally even overlap of layers, beginning at the proximal end of the residual limb and continuing to the distal end and allowing the excess elastic wrap to dangle beyond the end of the limb. This loose end is then threaded through the prosthesis in the same fashion as the tube pull stocking. At this point the donning process is very similar to the tube stocking method. The amputee stands on the sound limb allowing the residual limb with the elastic wrap in place to slip into the socket of the prosthesis as far as it will easily slide, the slack in the band being pulled through the valve housing until the amputee begins to feel the bandage starting to slide against the skin, at which point they begin the delicate control process of firmly pulling the elastic bandage through the valve housing as they gradually let the limb be pulled deeper into the socket. At the same time they must proceed carefully, as the bandage might fold and roll itself in a fashion called "roping". As the wrap begins to rope it can burn the skin tissue if it is extricated too rapidly. The same type pumping motion as used with tube stocking is useful in relieving pressures or burning as a result of roping.
Both a tube pull sock and an elastic wrap require an amputee to have very good standing balance, hand grip strength, arm strength, sound side limb strength, vision, mental acuity, patience and peripheral sensory perception.
Many amputees began to learn that the success of an adequate suction suspension did not mean they had to rely on only two methods of donning. Suction suspension is dependant on compression of tissue, called an interference fit. This tissue compression is what requires the use of a pull sock to overcome the friction that results from an interference type of fit. The main reason to use a pull sock to overcome this interference fit is because of dry donning. Amputees began to realize that lubrication on their skin would allow the residual limb to more easily and quickly slide into the proper interference fit without the use of a tube sock or bandage wrap. However, this method also has its limitations. The amputee must be able to stand and balance on a sound side limb. The residual limb must be able to withstand the pressures put on it to force it into the socket. This source of pressure is referred to as sheer force. Sheer force occurs when tissue is pulled in two different directions at the same time. In this situation the skin in contact with the inner surface of the prosthetic socket is pulling in the opposite direction that the residual limb is moving. The lubrication medium reduces this pull but cannot eliminate it. This drag on the tissue pulls the flesh tight over the distal end of the residual limb, which is the area where the incision line is located. Consequently, the tissue of the residual limb is pulled tight over the cut end of the bone with tissue that is scarred as a result of amputation surgery. The resulting incision and scar tissue is less flexible than normal undamaged tissue. Due to these factors the wet donning method of suction suspension is limited to the minority of amputees that can stand and balance on one sound side limb and are able to tolerate the pressures applied to their residual limb from the resultant sheer forces associated with wet donning.
Another donning method to receive widespread use is the roll-on silicone interface that incorporates an extended metal pin that fits inside a receiver at the distal end of the prosthetic socket for securely engaging the extended pin. This roll-on silicone material is approximately three millimeters thick. With both hands, the amputee has to roll the side of the interface into a shape resembling a condom. Donning of the silicone interface is basically the same as donning a condom. The inverted roll of silicone is properly placed in position on the end of the residual limb and held in place securely while the sides are rolled up onto the flesh, being careful to avoid trapping of any air between the interface and the skin of the limb. The patient must also take care to maintain the proper position of the pin end of the interface. Once the silicon interface has been completely unrolled onto the limb, the amputee is ready to finish the donning procedure by pushing the limb with interface and locking pin into the socket of the prosthesis until the locking pin engages the receiver. The amputee has to stand to finish the donning procedure. Standing allows the limb interface combination to fully compress into the socket, resulting in full engagement of the locking pin into the receiver. This method has allowed a larger number of amputees to effectively use suction suspension but has required additional schooling for prosthestists to learn a revised suction socket fabrication technique as well as revised suction socket fitting procedures. Still, there remains the greatest majority of amputees that lack significant strength, balance and coordination to don a suction suspension prosthesis, but who could use such a prosthesis only if they could don the prosthesis properly.
All of the aforementioned conventional suction socket donning techniques continue to elude successful use by the greatest majority of amputees--the geriatric amputee patient and those with other physical or mental infirmities. Many persons are classified as nonviable suction users due to arthritis of the hands, wrists, elbows or shoulders, arthritis pain or weakness in the sound side limb, bilateral amputations, heart problems, visual impairments, balance problems, back or hip pain and weakness that makes bending over difficult, or other problems such as difficulty in learning to properly use conventional techniques. These persons are denied the many advantages of suction suspension and are forced to settle for a less desirable form of prosthesis suspension.
3. The Patent Art
United States patent references of interest include U.S. Pat. No. 2,533,404 to Sharp et al., U.S. Pat. No. 2,569,790 to Whim et al., and U.S. Pat. No. 5,376,131 to Lenze et al. While these patents show various suction sockets arrangements and valves therefor, each discloses a conventional manner of introducing a residual limb into the suction socket (see column 4, lines 55-64, of the Sharp patent; column 4, lines 47-56, of the White patent; and column 4, lines 42-61, of the Lenze patent).
It is thus an object of this invention to provide a method for donning or doffing a suction socket that makes the use of suction sockets available to those persons who, by reason of physical or mental infirmity, are not generally recognized as candidates for this type of prosthetic suspension.